The present invention relates to plate-type heat exchangers which, in per se known manner, comprise a stack of a plurality of rectangular plates, each of which has an orifice in the vicinity of the apex of the rectangle, thus forming juxtaposed parallelepipedic racks, which are alternately traversed in countercurrent by cold fluid and hot fluid.
More specifically, the present invention relates to such plate-type heat exchangers which at the same time has an evaporator function and which are in particular used in heat pumps or in solar energy regeneration processes for evaporating a fluid with a low boiling point and making it expand in a heat engine.
Firstly, a general description of the construction of a per se known plate-type heat exchanger/evaporator will be given with reference to FIG. 1.
FIG. 1, which is a partial exploded view of part of such an exchanger, shows four adjacent rectangular plates 1, 2, 3 and 4 forming between them three parallelepipedic racks 5, 6 and 7 respectively. In the exchanger shown in FIG. 1 each of the plates 1, 2, 3 4 is provided with four orifices 1a, 1b, 1c and 1d for plate 1, 2a, 2b, 2c and 2d for plate 2 and so on, said orifices being located in the vicinity of the apices of the rectangle constituting the corresponding plate. As is also apparent from FIG. 1, these orifices aligned in the pile of plates are associated with tubular passages such as 8, 9 and 10 by means of which the corresponding orifices communicate with every other rack. The tubular areas 10 and 9 of the front face 11 of the drawing alternate with tubular areas 12 and 13 of the rear face 14. The same phenomenon occurs at the bottom of the exchanger where the tubular areas 15 and 16 on the side of front face 11 are staggered with tubular areas 17 and 18 of the rear face 14. The tubular areas can be made with a crushed joint on the side of the space between two consecutive plates. In racks 5 and 7 in the upper part of the represented exchanger portion there are horizontal plates or strips 20 which define two separate portions in each of said racks 5 and 7. These strips have a certain number of holes 21 along one of the adjacent plates.
The apparatus functions in the following manner. The cold fluid, which can for example be an easily volatilized compound such as freon, circulates in the upper part in accordance with the arrow F.sub.1 through the various aligned orifices and, after traversing the tubular areas 10 on the one hand and the tubular areas 9 on the other spreads into chambers 5 and 7 which are supply chambers located in the upper part. In said supply chambers, the cold fluid runs down the walls in the form of thin trickles after traversing orifices 21 and then penetrates the evaporation chambers 5a and 7a positioned immediately below the strips 20 of chambers 5 and 7. It is then heated in contact with the hot walls of adjacent racks and gradually evaporates, finally leaving in accordance with the arrow F.sub.2. However, the hot fluid enters and circulates in the apparatus in accordance with arrow F.sub.3, passes through the various racks such as 6 (every other rack as for the cold fluid) which are directly supplied and then passes out after being cooled in the upper part of the exchanger in accordance with arrow F.sub.4.
Thus, as is apparent from the drawing, the exchanger comprises two series of adjacent chambers, which are alternately cold and hot and in which the fluids circulate in countercurrent. The cold fluid is supplied by supply chambers which are separate from the evaporation chambers by means of strips 20 which bring about the separation of said two chamber types and by means of the outflow orifices 21 permits a distribution in the form of a cold fluid film along the adjacent hot wall.
It has been found, and this forms the object of the improvement according to the present invention, that it is possible to simply and effectively improve the operation of such an exchanger/evaporator, whilst eliminating certain disadvantages inherent in the principle thereof and which can be summarised as follows.
During the operation of a known exchanger/evaporator in accordance with FIG. 1, it has often been found that in the upper part of the apparatus, namely in the cold fluid supply chambers, there is a large amount of turbulence due to the start of boiling of the cold fluid. Attempts have been made to prevent this by providing surge tanks on either side of the separating strips 20. However, this has only reduced the phenomenon instead of completely eliminating it. However, this turbulence which increases with the temperature differences between two adjacent cold and hot compartments leads to premature boiling of the cold fluid prior to its introduction into the lower evaporation chamber, thus seriously prejudicing the regularity of cold fluid supply to the exchanger through the various orifices 20 and consequently reducing its efficiency.